1. Field of the Invention
The present invention relates to a waste water treatment apparatus and process. In particular, the invention relates to a water treatment system and process for treating storm and process water in the concrete industry.
2. Description of the Related Art
The ready-mix concrete and concrete-related industries create large amounts of excess water contaminated by high amounts of suspended solids and a pH level near, or above, EPA hazardous guidelines. The contaminated excess water is either in the form of process water or storm water. Storm water is created by rain or snowmelt carrying off yard waste. Plant equipment, slump-racks, tank-fill stations and truck mixer-drum washout produce process water. It is this mixer-drum washout that creates the majority of the contaminated water. Mixer-drum washout water is created when clean water and/or cleaning solution is pumped into a cement mixer to wash out the concrete waste. This waste contains rock, sand, cement, fly ash, and various admixture chemicals. While the rock and sand in the washout stream will settle quickly, entrained cementitious materials are difficult to remove. Cement is made up of finely ground limestone and clay that not only create the difficult-to-settle particulates, but also elevate the pH level of waste water to 12 and above.
The majority of concrete facilities rely upon settling ponds, pits, or tanks to separate coarse aggregate from the waste water. Such facilities may include a second pond or holding tank for receiving the waste water after settling either for re-use, or for pH neutralization prior to discharge. Some of the settling ponds may be of the evaporation/percolation type, wherein some waste water evaporates and other waste water percolates through to the surrounding ground. Eventually such settling ponds become trapped with a buildup of cementitious material, and must be cleaned with earth moving equipment that hauls the solid waste to a landfill, or is abandoned in favor of a new pit or pond. Where separation of materials is attempted within the plant, often the separators are mechanical clarifiers, using drag screws or rotating screws to mechanically separate the aggregate from the water. Screens have also been used.
To the extent that filtration has been attempted, traditional methods of filtration utilizing a barrier-type method have not been effective due to the nature and amount of cementitious particles, which will very quickly foul any known type of barrier media, which usually relies on gravity filtration. In addition to the cost of the barrier media, the amount of maintenance required has made this method uneconomical and ineffective. In addition to the barrier method, sand filters have and are being used. Once again, the clogging nature of cementitious materials renders sand filters somewhat ineffective and unsatisfactory. The cement particles cling to the sand granules and fairly quickly create an increasingly impervious surface layer. Since cement is ground to such a small particle size, some of the cement will still pass through the sand bed into the permeate stream. Furthermore, the flow rates of sand filtration systems are generally fairly low even, with fresh sand media.
While some producers use acids to reduce the high pH level in the contaminated water, they generally use a batch treatment method. In this method, the excess water is caught in some type of storage pit, tank, or container, and then enough acid is introduced to reduce the pH. Since the amount of acid required is dependent upon the amount of suspended solids in the water to be treated, non-filtered water requires an excessive amount of somewhat expensive acid.
Thus, methods of treating excess water in the concrete industry have often been limited to allowing the fluid to settle as much as possible in a settling pit, then simply allowing the remaining liquid to run off. The inventor is not aware of any prior systems or processes that effectively treat excess water from concrete production facilities. Various systems and methods have, however, been devised for treating other types of waste water.
One such process is exemplified in U.S. Pat. No. 5,320,755, issued Jun. 14, 1994 to Hagqvist et al. In this system, an incoming contaminated fluid is pressurized using a first pump and then passed through a filter in which the flow is divided into a filtrate or permeate flow, and a first bypass flow. The first bypass flow is recirculated using a recirculation pump. The bypass flow is provided to continually rinse the filtering membrane and prevent particulate buildup thereon. Between the filter bypass outlet and the recirculation pump is a pressure limiting valve to control the pressure in the filter and first bypass flow. At the outlet of the pressure limiting valve, the flow is divided into a second bypass flow which is returned to a point upstream the first pump, and a waste outlet. This system is not particularly suited for handling the large concentration of suspended solids present in excess water generated in the concrete industries. It would furthermore be desirable to provide a self-contained solution to the contaminated excess water problem.
U.S. Pat. No. 5,182,023, issued Jan. 26, 1993 to O'Connor et al., describes a process for treating arsenic-containing aqueous waste wherein the aqueous waste, treated, if necessary, to minimize the presence of materials which reduce the efficiency of reverse osmosis membranes, is passed through an ultrafilter to remove solids, followed by a chemical treatment to adjust the pH to range from about 6 to 8 and to add antiscalants and antifouling materials, which is then followed by subjecting the chemically treated filtrate to a reverse osmosis process to result in a permeate stream having less than about 50 parts per billion arsenic.
U.S. Pat. No. 4,999,116, issued Mar. 12, 1991 to Bowers, describes a waste water treatment process for the removal of heavy metals. The '116 waste water treatment process is optimized by continuously removing and filtering a sample flow of treated waste water subject to pH level control to determine the presence of remaining metals in solution to be precipitated. Filtering of the sample removes metals precipitated by pH level control.
U.S. Pat. No. 4,200,526, issued Apr. 29, 1980 to Johnson et al., describes a purification process for waste water from a textile plant and other manufacturing processes. After preliminary filtering to remove foreign particles, the waste water is treated with a reducing agent, if needed, and the pH is adjusted to 8.0-9.5. The waste water is then treated with a flocculating agent. After further treatment in a clarifier, the waste water is passed through a sand filter to remove any residual suspended solids. The pH is adjusted to below about 6.0 and the waste water is then subjected to reverse osmosis.
U.S. Pat. No. 3,909,405, issued Sep. 30, 1975 to Aoyama, describes a method for treating an acidic or alkaline waste liquid containing aluminum dissolved therein to convert it to a neutral liquid free from colloidal aluminum hydroxide. The aluminum is hydrolyzed in the presence of crystalline aluminum oxide. The crystalline aluminum oxide has an average particle diameter of about 0.5 to about 500 microns.
U.S. Pat. No. 5,264,132, issued Nov. 23, 1993 to Speranza et al., describes a method for removing ammonia, organic amines and alkaline impurities from waste water which comprises using a partially spent ion exchange resin which no longer meets the purity requirements for the production of methyl-tert-butylether (MTBE), washing the catalyst with water, contacting it with waste water, and removing the purified filtrate.
The April, 1997 issue of Pollution Engineering, published by Cahners Publishing Company, discusses membrane filtration in an article entitled, “Membrane Filtration: Live Long and Cost Less”, writted by Cathryn Hodson, which is incorporated herein in its entirety. Although no specific system is laid out, this article explains many known aspects of membrane filtration.
A web page entitled “Neutralization Chemicals including Neutralizing Acid, Base and Alkaline Chemicals”, published at least as of Dec. 17, 2003 by Wastech Controls and Engineering, Inc., teaches various chemicals and processes for neutralizing alkaline waste water.
None of the above disclosures, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a water treatment system solving the aforementioned problems is desired.